This study will evaluate for the first time the correlation between early changes in SUV and pCR in men and women with ER-negative, HER2-positive breast cancer receiving trastuzumab and pertuzumab (PT) pre-operatively. This has not previously been evaluated in patients receiving antiHER2 therapy alone and as such is novel and potentially practice changing. The results from this phase 2 biomarker study will be used to plan a randomized study using a predefined cut point for SUV decline such that the investigators can further attempt to identify a group of individuals with HER2-positive early breast cancer who do not require cytotoxic chemotherapy in addition to anti-HER2 agents. This non-invasive biomarker approach will be of great interest to breast cancer oncologists and patients by facilitating a personalized approach to managing patients with HER2-positive disease that will undoubtedly spare toxicity and reduce the costs associated with anti-cancer strategies, without compromising efficacy.